One process of making a liquid fabric softening composition is by mixing the components of the composition using cavitation. Cavitation refers to the process of forming vapor bubbles in a liquid. This can be done in a number of manners, such as through the use of a swiftly moving solid body (as an impeller), hydrodynamically, or by high-frequency sound waves. When the bubbles collapse further downstream from the forming location, they release a certain amount of energy, which can be utilized for making chemical or physical transformations.
One particular method for producing hydrodynamic cavitation uses an apparatus known as a liquid whistle. Liquid whistles are described in Chapter 12 “Techniques of Emulsification” of a book entitled Emulsions—Theory and Practice, 3rd Ed., Paul Becher, American Chemical Society and Oxford University Press, NY, N.Y., 2001. An example of a liquid whistle is a SONOLATOR® high pressure homogenizer, which is manufactured by Sonic Corp. of Stratford, Conn., U.S.A.
Processes using liquid whistles have been used for many years. The apparatuses have been used as in-line systems, single or multi-feed, to instantly create fine, uniform and stable emulsions, dispersions, and blends in the chemical, personal care, pharmaceutical, and food and beverage industries.
It has been found, however, that improvements to such methods are desirable. Current processes utilizing liquid whistle apparatuses require the liquid(s) intending to be mixed, to enter the liquid whistle under very high operating pressures, in some cases up to 1000 bar. By operating pressure, it is understood to mean the pressure of the liquid(s) as it enters the liquid whistle device. This ensures efficient mixing of the liquids within the apparatus. However, achieving such high pressures is expensive, energy consuming, and requires the use of large bulky equipment, such as the Sonolator® High Pressure Homogenizer. Another problem with such high pressures is that they can cause erosion of components within the mixing device. This is usually due to mechanical wear caused by the high pressure liquids, but can also be exacerbated by the chemical properties of the liquid(s) being mixed.
There is a need in the art for improvements to processes for making fabric softener compositions by producing shear, turbulence and/or cavitation, such that lower pressures can be used, yet the same degree of mixing can still be achieved as is seen with alternative high pressure apparatuses.
There is also a need in the art to minimize the erosion of internal components of high pressure mixing apparatuses.
It was surprisingly found that the methods of the present invention, which comprise mixing a fabric softening active in liquid form with a second liquid composition using an apparatus comprising two or more orifices arranged in series, achieved a comparable or better degree of mixing as is seen with known shear and/or cavitation mixing methods, but required decreased pressures than are normally required.